1. Field of the Invention
The invention relates to an image recording apparatus equipped with means having an aperture portion that serves to modulate particle flow of charged toner and, particularly, to an image recording apparatus suitable for a copying machine, a printer, a plotter, a facsimile machine, or similar applications.
2. Description of Related Art
As one known image recording apparatus, there has been conventionally proposed an image recording apparatus in which an image signal is applied to an electrode having plural opening portions (hereinafter referred to as "apertures") to modulate the passage of toner particles through the apertures. An image is recorded on a support medium disposed on a counter electrode in accordance with the image signal. Such an image recording apparatus is disclosed in U.S. Pat. No. 3,689,935, for example. This image recording apparatus includes an insulator (insulating layer), a shielding electrode in the form of a continuous body which is disposed on one of the opposite surfaces of the insulating layer, and plural control electrodes which are insulated from one another and located on the other surface of the insulating layer. The apparatus also includes an aperture electrode unit having at least one row of apertures which are provided in correspondence with the respective control electrode so each aperture penetrates through the three layers of the insulating layer, the shielding electrode and an associated one of the control electrodes, a voltage applying means for applying selected electric potentials between the shielding electrode and each of the control electrodes, a toner carrier for supplying charged toner particles so that the flow of the toner particles passing through the apertures is modulated by the applied potentials, and means for moving the support medium relative to the aperture electrode unit to position the support medium in the path of flow of the toner particles.
In the conventional image recording apparatus as described above, the flow of the charged toner particles is controlled by the electric field inside the apertures. Thus, the electric field outside of the apertures is very weak. Accordingly, the toner particles supplied to the lower side of the apertures are attracted into the apertures by a weak electrostatic force, so that a flow amount of toner particles passing through the apertures per unit time is small, and the image forming speed is slow. Further, in order to improve controllability of the passage of the toner particles through the apertures, the electric field inside of the apertures must be intensified requiring an expensive high-voltage driving element.